This invention concerns glycolic acid terpolymers with a dihydroxyalkane and a dibasic acid. The terpolymers have been found to have improved flexibility, lower melting points, and excellent adhesive properties.
Glycolic acid polymerization is described in U.S. Pat. No. 2,676,945. According to this patent, the polycondensation is carried out in the solid state by heating glycolic acid at 218.degree. C. and 0.5 mm pressure.
U.S. Pat. No. 2,585,427 describes melt polymerization of glycolic acid at 197.degree.-245.degree. C. and 0.3-0.5 mm pressure using an antimony catalyst.
Polyglycolic acid, or "polyglycolide", as it is sometimes called, has a variety of uses. In particular, being soluble in physiological fluids, it has been used as an absorbable suturing material. To enhance or alter the physical properties of polyglycolide, numerous glycolic acid polyester copolymers have been suggested. For example, polyglycolide has been copolymerized with low-molecular-weight lactones such as beta-propiolactone to form heat-stable copolymers. British Pat. No. 695,823 describes moldable, high-tensile-strength polymeric organosilicons prepared by copolymerization of alkyl and aryl dialkoxyhalosilane mixtures with glycolic acid or polyglycolide. Belgian Pat. No. 584,365 describes flexible film-forming copolymers prepared by heating glycolic acid with a maleic anhydride-vinyl acetate copolymer. U.S. Pat. No. 2,916,468 describes textiles treated with a copolymer of polyglycolic acid and a polyalkylene glycol such as polyethylene glycol or methoxypolyethylene glycol.
Polybasic acids and polyhydric alcohols have been copolymerized to form polyesters often referred to as "alkyd resins". When both the acid and alcohol are bifunctional, the polyester is a linear copolymer. In general, the linear polyesters of a dibasic acid and a diol are microcrystalline powders. In the molten state they are usually quite viscous. Many of these copolymers are described in Advanced Chemistry, Vol. I, Gilman (ed.), John Wiley and Sons, Inc.